Hi Mojo
Welcome to the forum from New Zealand.
A couple of really useful links for you if you are new to the world of Z3 ownership:
- NewTIS is the BMW database of maintenance procedures and wiring diagrams etc
https://www.newtis.info/tisv2/a/en/
- Z3 wiring diagrams can be found in this forums Resources section. Use your build date to select the correct set of diagrams
https://zroadster.org/resources/
- RealOEM is the source for part numbers and exploded diagrams
www.realoem.com
Now for your question on the sub-frame.
- Go to RealOEM and enter the last 7 digits of your VIN number and hit search.
- Bookmark the page for future use.
- Browse parts
- Rear axle
- Find the diagram with the sub-frame in it and click on it
- The sub-frame (rear axle carrier) is item 1, scroll down and click on the part number
- Click on "Z3 E36" and you will get a list of models that share the same sub-frame.